Regenerative braking system for electric motors.



UNITED STATES PATENT OFFICE.

NORMAN W. STORE-B, OF PITTSBURGH, PENNSYLVANIA, ASSIGNOR 'I'OWESTINGHOUSE ELECTRIC AND MANUFACTURING COMPANY, A CORIORATION OFPENNSYLVANIA.

BEGENERATIV E BRAKING SYSTEM FOR ELECTRIC MOTORS.

Application flied October 5, 1912, Serial No. 724,068.

To all whom it may concern.-

Be it known that I, NORMAN W. STORER, a citizen of the United States,and a resident of Pittsburgh, in the county of Allegheny and State ofPennsylvania, have invented a new and useful Improvement in RegenerativeBraking Systems for Electric Motors, of which the following is aspecification.

My invention relates to systems of electric motor control and it hasspecial reference to such systems as are adapted for use in electricrailway service.

The object of my invention is to mate rially increase the efiiciency ofanelectric railway distributing system, by eifectively utilizing theenergy, usually dissipated in the form of heat, which is released whenrailway vehicles are brought to rest from relatively high speed or arerun down hill with the brakes set.

Anotherobject of my invention is to pro vide a system of the aforesaidclass, that shall embody means for utilizing and regulating the electriccurrent generated in the motor armature-s during the braking period, forefficiently retarding the car or locomotive with which the system isemployed.

Another object of my invention is to provide automatic means for soregulating the field excitation of the motors during the braking periodas to maintain a substantially constant braking current, While the motorspeed is constantly decreasing.

Another object of my invention is to provide a system of control forrailway vehicles for automatically governing a plurality of electricmotors by connecting them successively in series and multiple circuitrelation in order to accelerate the vehicle, and automatic means forindependentlv connecting the motors across the supply circuit, when thevoltages generated in the motor armatures during the braking period bearpredetermined relations to the voltage of the line, whereby energv maybe supplied to the line in retarding the vehicle.

Another object of my invention is to so associate an ordinary pneumaticbrake equipment with a regenerative braking system, as to automaticallyapply the pneumatic brakes and to interrupt the regenerative circuitwhen the speed of the vehicle falls below a predetermined value.

A further object of my invention, 13 to Specification of Letters Patent.

Patented Nov. 6, 1917. Renewed September 7, 1916. Serial No. 118,951.

provide a regenerative control system wherein the above-mentionedauxiliary brake apparatus automatically b comes effective upon the lossof the electric braking effort, by reason of the trolley leaving theoverhead wire, for example.

While my invention is particularly adapted for the control of railwayvehicles, it is not limited to any class of service and may be utilizedin'the control of automobiles and other road vehicles or in the controlof cranes, hoists and other electrically operated devices.

When a large number of carsor trains are operated under ordinary railwayservice conditions in a confined area as, for example, in thesubway of alarge city, there is a large amount of energy dissipated in the form ofheat in frequently retarding the cars or trains by the application ofairbrakes or any other of the well known braking appliances which havehitherto been available for this service. This energy is not onlywasted, but becomes a verv serious menace to the operation of thesystem. This is particularly true during the summer months whenrelatively high atmospheric temperatures prevail. In many cases, theheat in tunnels and subways becomes almost unbearable to passengersa-ndnecessitates the addi' tionalexpenditure of large quantities of energyin providing cooling and ventilating apparatus. Furt ermore, thecapacities of electric driving motors are reduced by reason of the factthat they operate in atmosphere at high temperature, and it is evidentthat the problem is a very serious one.

It has been my'aim to provide a practical. arrangement capable ofapplication to either a single ear or to a plurality of cars controlledin multiple for automatically returning energy to the supply circuit ofthe system during the braking or retarding period of the vehicle orvehicles to which it' is applied. I

In order to adapt the system of control for this class of service and tosecure a maximum braking efl'ort without injuring the electric motors orthe other apparatus with which the vehicle is equip ed, I have providedautomatic means, in t e form of a dif' ferential relay switch, forautomatically connecting a propelling motor to the supply circuit whenthe eleetromotive force genwhich,

erated at its terminalsbears a predetermined relation to the voltage ofthe supply circuit.

I. also provide automatic means for regulating the field excitation ofthe 'motor during the period when it is acting as a generator whereby asubstantially constant braking current is delivered to the su plycircuit. In addition to the foregoing, fiiave so interlocked the variouscontrol switches and-apparatus of the system as to permit of the normalseries parallel operation of the motors in accelerating the vehicle, byadjusting the master controller in one direction, and of automaticadjustment of the circuits for re enerative braking accompanied byindepen entconnection of the motors to the circuit at the proper time,by throwing the master controller in the opposite direction or b using asecond master controller.

By ut' ing the regenerative braking system in combination with theordinary air brake apparatus, a large proportion of the energyordinarily lost in heat is returned to the supply circuit, while, at thesame time, the regenerative braking system is not relied upon when thespeed of the vehicle is below a predetermined value. Consequently, thestop is accomplished in a length of time and each of the two methods ofbraking is employed when it is. most efiective. The brake shoes arematerially relieved from wear and will, of course, require veryinfrequent renewal.

Figure I of-the accompanying drawings is a diagrammatic view of a systemof electric motor control embodying my invention, the main circuitconnections and the switches and control apparatus which are directly'amociated therewith being shown complete according to the usualdiagrammatic methods of representation. The control circuits are,however, merel indicated by appropriately designated es in order-toavoid confusion.

Fig. 2 is a diagrammatic view of the control circuits inc uding theactuating coils and the interlocks which form parts of the main circuitswitches and control ap aratus shown in Fig. 1. ,In order to simp ifythe circuit connections, however, the intcrlocks as shown in Fig. 1, aregrouped with the various switches, are distributed and each of them ismarked to indicatc the switch or control device with which it isassociated and by which it is operated.

Fig.3 a simplified diagra of the mam are t of the auxiliary circuitconnections during the period of re enerative braking.

Referring to i'g. 1 of the drawin the system here shown comprises a suppy circuit conductor which, for convemence, is marked Trolley a returncircuit conductor which is marked Rail; a pair of ilarly,

mmatic view connections and certam' electric motors having armaturesmarked re spectively M#1 and M#2 and field magnet windin markedrespectively F1 and F2; two pair of line switches marked LS1, M1, LS2and M2; a resistor section used' only when the motors are connected inseries relation and adapted to be short circuited by a switch S, aplurality of resistor sections one of which is short circuited by aswitch R1, two of which are short circuited by a switch R2 and all threeof which are short circuited by a switch R3; a second group of resistorsections, one of which is short circuited by a switch RBI, two of whichare short circuited by a switch BB2 and all three of which are shortcircuited by a switch BB3; a pair of field resistances FRl and F112which are respectively provided with short circuiting switches X1 andX2, storage batteries marked respectively Bat. 1 and Bat. 2; a ofgovernin the field resistances, marked K1 and PK2; a lurality of limitswitches comprising A1, 1, C1 and L in one group, and A2, group, a triprela switch T, a plurality of control switches J and G, difierentialrelay switches D1 and D2 and a reversing switch marked Reverser.

In order to avoid confusion, each resistor section will hereinafter be dby the reference character which is applied to its short circuitingorexclu switch for example The resistor short clrcifited by the switch Swill be termed the S resistor. Simone of the motors will be referred toas motor M 1, which is the reference character applie to its armature,and the other as motor M#2.

' The operation of the system, with referencetothemaindreuitscmlwillfirstbe discussed and, so 'tlv control circuits, by which the esimdcircuit changes are accomplished, will be traced.

Assuming that it is desired to accelerate the motors, switches LS1 andLS2 M1 and JR, X1 and X2 are first closed. switches closed, a circuit isestablished from the trolley through a main circuit conductor 70, theswitches LS1 and M1, the series resistor S, he conhcts 71 and 72 of therevel-set, the field magnet winding F1, reverser contads 73 and 74conductor 75 the switch XL; conductor V coils of the hmit switchmAl, B1,C1 and L, resistor sections B3 B2 and B1, 9. conductor 77, the switch 33a r 78, resistor sections BB1,

field magnet winding F2, 82 and 83, a'conductcr 79, the switch conductor84, coils of the limit switches vB2and C2, the coil of the trip switchB2 and C2 in another like and BB3, the ar'-'. mature M#2, reverse:-contads 801ml 81,-the.

for V With-these In operation, only with all of the resistor sectionsincluded in the circuit, with the exception of the field regulatingresistor sections FRl and FR2 which are short circuited.

In the second to the eighth control steps inclusive, the switches S,RRl, R1, RR2, R2, RR3 and R3 are successively closed, gradually shortcircuiting the resistor sections and connecting the, motors directly inseries across the line.

The next three are transition steps in which the switch J is firstclosed, completing the short circuit connection from the conductor 76 tothe armature M#2, the switches RRl to R3 inclusive, and switch JR arenext opened, and finally the switches M2 and G are closed.

In the ninth regular step of the controller, the switch J is permittedto open, leaving the two motors in parallel across the circuit, with theresistor sections R1, R2 and R3 in series with one of them and thesections RRl, BBQ and. RR3 in series with the other.

In the subsequent accelerating steps, the resistor sections RBI to R3,inclusive, are short circuited, leaving the motors in parallel relationdirectly across the circuit.

There are only two braking steps, one marked braking, and the otherholding. the braking step will be utilized if the vehicle is to bebrought to rest, but, if it is only desired to slow down the vehicle orto hold it in descending a grade, the holding step may be utilized.

The braking step closes the switches M1, G, M2, S, R1 and RRl and movesthe controllers PKl and PK2 from their off positions into theirpositions 1. By these means the switches X1 and X2 are opened and alurality of switches Y1 and Z1 and Y2 and 2 are closed.

Inasmuch as the line switches LS1 and LS2 are open, the motors are notconnected to the line but Bat. 1 is connected in shunt relation to thefield magnet winding F1 and the field regulating resistance FR1. Bat. 2is similarly connected in shunt to field magnet windin F2 and the fieldregulating re sistance F 2.

The line switches LS]. and LS2 are automatically and respectivelydependent upon the difierential relay switches D1 and D2 and,consequently, when a predetermined relation exists between the voltagesgenerated at the terminals of the respective motor armatures and thevoltage of the line, the mo- ,tors are automatically and independentlyconnected to the line by the closing of the corresponding line switchesLS1 and LS2. After the motors are connected to the circuit, thecontrollers PKl and PK2 are automatically regulated, as hereinafterpointed out, to so govern the field regulating resistances, with whichthey are associated, as to mainsure is admitted from tain asubstantially constant braking current. This obviously involves thegradual exclusion of the regulating resistances in order to maintainsubstantially constant generated voltages at the terminals of the motorsas their speeds decrease.

In the holding position, the actuators for the PK controllers areprevented from continuing to exclude the re ating resistance and,consequently, the br g effort exerted by the motors will decrease withthe instead of continuing constant. In the case of descending grades;the speed will vary until the motor tractive efl'ort just balances theaccelerating effort corresponding to the difference between trainresistanw and grade acceleration, when the speed will remain constant.

The PK controllers are intended to be representative of any suitablemeans for automatically governing the field regulating resistances and Ido not wish to be limited to any specific control apparatus Each of thePK controllers comprises a plurality of contact fingers 86, which areconnected to intermediate points in the field.

regulating resistor with which it is 8S0- ciated; suitable contactsegments 87, which are adapted to successively the fingers 86 andgradually short circuit the resistance in a well lmown manner; contactmembers 88 and 89, which form parts of the switches Y and Z, and a.plurality of interlockingcontact members and cooperating therewith,which will be referred to in detail in the discusion of the controlcircuits.

Each of the controllers is preferably in the form of a drum, which isshown developed into a single plane in awell known manner, and isprovided with a. shaft 90 to which a pinion 91 is secured. Each of thedrums is actuated by a rack 92 which meshes with its pinion 91 and isconnected at its respective ends to pistons 93 and 94 which operate incylinders 95 and 96. Fluid presa tank or reservon- 97, through anelectromagnetically controlled valve 98, to the cylinder 96, when anaictuab ing coil 99 for the valve is decnergized, and fiuld pressure isadmitted from the tank or reservoir to the cylinder 95 when anactuatergized.

The arrangement of parts is such that if both magnet valves aredenergized, fluid pressure will'be admitted through the valve 98 to thecylinder 96 and will so actuate the istons 94 and therack 92 as to throwthe EK drum, with which it is associated, to its off position.

If valve magnet 101 is energized, fluid premure will be admitted to thecylinder 95 but no motion of the drum will result, inasmuch as thepressures are then balanced on mg coil 100 for the magnet valve 101 isenment of contact the two sides of the piston member. A motion of thedrum may, however, be produced by subsequently energizing the coil 99 ofthe valve 98, since, by this means, the valve 98 will cut oil the supplyof pressure from the reservoir and will open its exhaust port. The drummay be stopped at any position by merely denergizing the coil 99, and itmay be returned to-its off position by merely deenergizing both of thecoils 99 and 100.

The valve magnet 101, which, when energized, is open to admit fluidpressure to the cylinder and, when denergized, is closed to exhaust airfrom the cylinder, will hereinafter be referred to as a standard valvemagnet, while the valve magnet 98 which is open to admit fluid presureto the linder when de'nergized, and exhausts the air from the cylinderwhen energized, will hereinafter be referred to as an inverted'valvemagnet.

The reverser may be of any suitable but preferably comprises a sectionwhich is adapted to occupy two positions, one for forward and the otherfor reverse operation of the vehicle. It is preferably pneumaticallyoperated, and is controlled y valves having actuating coils 102 and 103.

The limit switches'Al and A2 are closed when one above a predeterminedvalue, and t e switches B1 and B2, C1 and C2 and L are opened whenenergized above predetermined values.

Each of thedifierential relay switches D1 and D2 is provided with a coil104 which, when energized, tends to raise it, and a coil 105 which tendsto hold it down.

The coils 104: are respectively connected in shunt relation to thearmatures M#'1 and M#2 when the PK drums occup 1 to 8, inclusive, byreason of th fingers 106 with a contact member 107.

The coils 105 are similarly connected across the supply circuit when thePK drums occupy positions 1 to 8, inclusive, by

reasonof the engagement of contact fingers 1 8 a contact member 109. r

The other switches of the system are adapted to occupy two positions,one in which the main interrupted, hereinafter called the switch outposition, the

- other in' which the switch is closed and the circuit is completed,hereinafter called the switch in poaition. Each of the switchesisclosedwhen itscoilisenergized.

The switches may be, and preferably are, actuated pneumatically, the0011 respectigely associated with the switches being a a flui presure toc linders for closing the switchw'in a well o'wn manner. In-fact, theconstruction of the main switches forms no part of my present inventionand they "the motors are connected positions e engage-- gted merely toopen valves to admit may be actuated directly or indirectly, in ansuitable manner.

ferring to Fig. 2 of the drawings, the control circuits here shown aregoverned by a master controller adapted to occupy an .oif position,accelerating positions 1,2

and 3, a braking position and a holding position; and a master reverseradapted to occupy a forward position f and a reversinglposition r.

nergy may be supplied to the control circuits andauxiliary apparatusfrom any suitable source, such as a control battery having a positiveterminal which, together with its connected conductors, is marked B+ anda negative terminal which, with its connected conductors, is marked B.Obviously, Bat. 1 and Bat. 2 may be employed forthis purpose, ifdesired. a

The arrangement of circuits is such that if the master controller ismoved to its position 3, the motor acceleration will progressautomatically until the motors are finally connected across the line .inmultiple circuit relation. If it is moved only to position 2,'theacceleration will progress until 'across the line in series relationand, if moved only to sition 1, the motors will be connected in seriesrela-; tion across the line with all of the acceleratresistance inprogrescording to the will of; the operator or motorman.

Assuming that the master controller is '2 moved directly from its ofi'position to its accelerating position 3, that the master reverser hasbeen'thrown into its position f, .and that the reverser occupies theposition r,

a control circuit is'established from-the control battery terminal andconductor B+, thro a control cutout switch which is cl a contact fingerfof the! master reverser, a conductor f, a contact member 4 of themaster controller, a. control wnductor 4, contactfmember 110, a coil fof the reverser, a conductor 49, and M1-out, to conductor B--.v Anothercircuit is established from conductor B+, contact fingers B+ and.

2 of the master controller, control conductor 2, PKl-ofi, actuatin coilof switch LS1, conductor 47, throu the trip relay T to B. From controlconductor -2 another circuit is established .throu h PK2-.-6lf,conductor 48, coil of 2,

conductor 47, and the'relay switch T toconductor B-. Thus, tlm reverseris thrown to position f, in.which position it is shown, and the elm Acontrol circuit is established through the contact member; 110, tocontrol conduc- 180 tor B, from which point circuit is completed lineswitchesLSl and L S2 are 7 through the actuating coil of the switch M1,conductor 12 and the relay switch T to conductor B. A circuit is alsoestablished from conductor B, through contact member 111 of the switch Jout, through conductor 23, contact member M2'-out, conductor 24, contactmember PK2ofi', conductor 25, contact member PKl-ofi', conductor 26,

and the actuating coil of the switch JR actuating coil of the switchRRl.

to conductor 12, c1rcuit being completed as before. This switches M1 andJR are closed as soon as the reverser and the master reverser occupycorresponding positions.

The closing .of these switches connects the motors in series relationwith the various resistor sections included as above indicated. Thecurrent traversing the motor circuit is sufiicient to raise the limitswitch L in a well known manner. As soon as it is again closed by reasonof the increased speed and counter-electromotive force of the motorarmatures, another control circuit is established from finger B+ of themaster control, through finger and control conductor 1, through thelimit switch L, a conductor 20, contact member M1in, a conductor 21,contact member JR-in, conductor 27, and the coil of S-limit to conductor12. The switch S is thus closed, its coil being transferred in a Wellknown mannor from the actuating circuit just described, to a holdingcircuit established from the conductor B, through contact member 112.The actuating'circuit which was completed through the coil of the switchS is now completed through contact member S--in, conductor 28, contactmember 113, and the This actuatingcircuit, however, is not completeduntil the limit switch L is again closed, pro vided the rush of currentin the main circuit, produced by the, exclusion of-the resistor S, hasbeen sufiicient to open it.

Similarly, the coils of the switches R1, BB2 R2, BB3 and R3 aresuccessively energized and transferred to the holding circuit 1nmultiple relation, the said holding circuit extending through contact'member 11 of switch J-out.

As soon as the B3 switch is in, a circuit "is completed from controlconductor 3,

through contact member R3in, conductor 44, member G-out, conductor 45,and the actuating coil of the switch J, to the conductor 12. The switchJ, which completes the bridging circuit above referredto, is thusclosed. .In closing, it so actuates the contact member 111 as tointerrupt the suply of energy to the holding circuit conductor 23,thereby permitting the resistance switches BB1 to B3,- inclusive, andthe With the switch JR open, a circuit is established, dependent uponthe limit switch L through contact member M1-in, conductor 91, contactmember JBPout, conductor 22, and the actuating coils of theswitches M2and G to conductor 12. When the switch G is closed, the circuit throughthe actuating coil of the switch J is interrupted and, consequently,switch J is opened and the motors are connected in multiple circuitrelation, the resistor sections R1, R2 and B3 bein included in serieswith the motor M1 an the resistor sections BB1 BB2 and BB3 beingincluded in series with the motor M#2. It will be observed that theholding circuit of the switch S is inde endent of the position of theswitch J, an conse uently,

The resistor sections are again short circuited, dependent upon thelimit-switch L, a substantlally balanced relation being maintainedbetween circuits of the two motors by reason of the fact that theswitches, which close in succession, are selected alternately from thetwo groups. The switch JR remains open on'account of the contact memberM2out, which makes it impossible to close both the switches JR and M2 atone time. This is particularly important since the switch IR will'shortcircuit the line if it is closed when the switches M1, M2 and G areclosed.

Assuming that the vehicle propelled by the motors M#1 and M#2 isoperating at or above a'predetermined rate of speed, and that the mastercontroller'is returned to its oil position, permitting all of theswitches to open, and is moved -.to its braking osition; under theseconditions, energy is rst supplied from the B+ finger of the mastercontroller to a finger-8, one circuit being completed through controlconductor 8, contact member R3-'out, conductor 52,? contact memberPK1ofl, and conductors 56 and 58 to the actuating coils 99 and 100 ofthe valve magnets which are associated with the controller 'PK1. Anotherpair of circuits is established from conductor 8,

through a.- contact member RR3 out, c onductor 53, a contactmemberPK-2ofi, oonpositions into their positions 1, in which the circuitsthrough the inverted valve magnet coils 99 are interrupted, and thecircuits through the standard valve magnet coils 100 are maintained, byreason of the peculiar shapes of the contact members PKI and. PK2 thatare included in the said circu ts.

Full pressure exists in each of the cylinders 95 and 96 and,consequently, the controllers remain in position 1. Another circuit isestablished from the finger 13-1- of master reverser, through a. contactmemher and a conductor f which is now connected through a contact member114 of the master controller to finger 5, circuit being completedthrough the conductor 5, a contact member 115 of the reverser and amagnet coil 1- to the conductor'49, from which point circuit iscompleted through contact member M1out to conductor B-.

The'reverser is thus thrown to the. opposite position, although'theposition of the master reversefhas not been changed.

Energy is then supplied through the contact member 115 to the controlconductor R and the coil of the switch M1 which is, consequently,closed. Another circuit is established, since the PK controllers occupytheir positions 1, from the conductor R to either contact member PK1--1to 8, or contact members PK2-1 to 8, to conductor 22, from which pointcircuits are completed through the coils of the switches M2 and G to theconductor 12. As soon as the switches M2 and G are closed, a circuit isestablished from the conductor B, through contact member G-in, conductor21, contact member M2-in and conductor'27 to the actuating coil of theswitch S.

The switch S then closes and ener is supplied sncce$ively to the coils othe switches BB1 and B1. The resistor sections S, RBI and R1 will thusbe short circuited. The closure of the switches will not groceed as inthe case of acceleration from 1 to R3, inclusive, by reason of thecontact member PK2-ofi, which is introduced between conductor 30 andconductor 31. At this sta of the control operation, a connection )8established, although the circuit is not completed because the switchLS1 is open, from one terminal of line switch LS1, through the switchM1, which is closed, the swltch S, the motor armature M#1, the fieldmagnet win F1, in the reverse direction, the resistor FR whichwasintroduced when the controller PKl moved into its position 1, the coilsof the limit switches A1, B1, C1 and L, the resistor sections B3 and R2and theswitchGtothe'raiL' 1 r The field magnet win F1 and the resistanceFBI are bridged Bat. 1, since the switches Y1 and Z1 are cl osed in thisposition of the controller 'PKl. The motor M#2is similarlyconnectedwithreferenceto the controller PK2 and the rkefilatingzi'p sistance FR2,resistor sections and being included in the connection. Circuit is notestablished, however, since line switch" LS2 is open.

The storage batteries serve to excite the field magnet with which theyare associated, and inasmuch as the vehicle'is assumed to be operatingat a relativelyhigh speed, the motors will act as mentors the voltagesof which are depen ent upon the speed. When the circuits are in thecondition just" described, however, the generated electromotive forcesare somewhat lower than the electromotive force of the supply -line and,consequently, the differential relay troller PKI is energize fromconductor 54,

through contact member LS1-out, conduc tor 65, limit switch C1,conductor 58 and the standard valve ma et 100 of the controller PKl toconductor As soon as both of thevalve ma and 100 are energized,thecontro' er'PKlwill move from its first position, throu h its second,third and fourth, etc., gradual y 'exets 99 cludin the field regulatingresistance FRl from t e circuit until the voltage generated at theterminals of the motor armature reaches a predetermined value, which isin excess of the line voltage at least by an amount equal to the batteryvoltage, when the difl'erential relay switch D1 will be raised. As soonas this occurs, the circuits just traced through the controller PKI, andthe valve magnets 99 and 100 are temporaril interrupted. A new circuitis establis ed from conductor 8, through conductor 52, R3-out,difi'erential relay contacts DlA, conductor 57, contact member PK11 to8, conductor 46, the actuating coil of the line switch LS1 and aconductor 47, which is connected to the ne tive conductor B1 throughthe-relay switch T, SwitchLSl then closes and motor M#1 is connected tothe supply circuit with the resistor sections R2 and R3 included tolimit an excesthe PK drum by a friction clutch connection. Thearrangement of parts is such that a predetermined backward movement ofthe drum is produced, irrespective of its position when thedifi'erential relay switch is raised, until the contact segment 117bridges the gap in the circuit of the standard valve magnet that wascaused by the removal of the contact memiber LS1-out, when the. switchLS1 closed. The other gap in the circuit, namely, that at. the contactmembers D113, is closed by a contact member LS1-in as soon as the switchLS1 closes. The standard valve magnet coil is thus energized, and

the PK controller is held balanced in whatever position it thenoccupies. It should be noted that the contact segment 117 issufliciently wide to bridge the space between the 011' position andposition 1, thereby preventing the PK controller from dropping backbeyond its first on position which would entail the opening of the lineand motor circuit switches.

The backward movement of the PK drum reinserts a certain amount of thefield regulating resistance FR-l, just at the time when the motor isconnected to the line. This is particularly important because thedirection of current in the battery is immediately changed since it isconnected in series relation to the motor armature, by the brakingcurrent. Its voltage is, therefore, suddenly raised and the field magnetwinding F1 is,

V consequently, very much strengthened, and

tends to suddenly increase the braking current. Just suiiicient fieldregulating resistance, however, is reinserted to decrease the fieldstrength and thus avoid excessive rush of current and excessive armaturevoltage. It is evident from the foregoing that the battery holds thefield current substantially constant and either supplies energy to thefield or absorbs the difference between the field current and thearmature current in effecting this regulation. Since the battery isbeing charged during a part of the time it is in operation, its capacitymay be relatively small.

As soonas the PK drum comes into action after the motor has beenconnected to the line and the reduction in motor current has permittedthe limit B1 to drop, the resistors R2 and R3 are excluded from circuitprogressivel and in accordance with the action of the imit B1 by theclosure of the correclosed, provided the resistance switches R2 and R3are also closed, a circuit is established from the conductor 54:,through the aforesaid limit switch, conductor 55, con tact memberLS1-in, conductor 35, contact member PK1-l to 8, conductor 33, contactmember R2 in, conductor 36, contact member PK1-1 to 8, conductor 37,contact mem ber R3-in, conductor 40, interlock PK1--1 to 8, conductor11, contact member LS1-in, conductor 56 and the magnet coil 99 toconductor 9.

The inverted valve magnet coil is thus energized whenever the limitswitch B1 is closed and, consequently, permits a series of forwardmovements of the controller sufficient to reduce the field regulatingresistance FBI and to keep the braking current in excess of 120 amperesor some other predetermined value.

If the braking current should, when the resistance switch R3 is in,exceed a predetermined higher value, such as 160 amperes, the limitswitch Cl W11]. open and will suddenly bring the controller to rest..This action is effected by contact member 119 which is connected inshunt to the limit switch C1 and is limited to a very small movement bya stationary stop 120 and is connected to the drum by a friction clutchconnection, the arrangement of parts being such that it requires a verysmall backward movement of the drum to re-establish a balanced conditionbetween the pressures in the. cylinders 95 and 96.

Thus, it is evident that the limit switches B1 and C1 hold the brakingcurrent within a predetermined value, irrespective of the speed at whichthe motor is operated. Under normal braking conditions, the regulatingresistor FBI will, of course, be gradually excluded until it is entirelyshort circuited.

When either of the controllers PK occuies its position 8, a circuit isestablished mm the finger B+ of the master controller through a fingerw, a conductor w one or both of a pair of contact members PK18 andPK2-8, a wire 13.0 and a coil 131 of-a relay switch 132 to the conductorB-, switch is closed, a holding circuit is estab lished from theconductor a: to the conduct0r'130, independently of the controller PKthrou h an upper pair of contact members 133 o the switch 132.

A lower air of contact members 134 are also bridged when the switch isclosed and com lete a circuit from conductor B+ to con uctor B- througha coil 135 of a magnet valvel36. This valve, when ener zed, closes anexhaust ort 137, opens an a i sion ort 138 and admits pneumatic pressureom a; tank or reservoir 139 .to. a brake cylinder 140.

This cylinder and valve are intended to When the represent any wellknown system of pneumatic brakes which may be independently controlledin the usual manner but which are automatically applied when either ofthe controllers PK occupies its position 8.

The circuit through the :0 wire is, of course broken when the mastercontroller is returned to either its holding or its ofi? position.

When the mechanical brakes are ap lied, the regenerated braking currentwll l, of course, diminish rapidl as the motor s eed is-reduced.Finally, w en the speed 0 the vehicle reaches a relatively low value,'such as, for example, 12 miles an hour, the A1 limit switch will falland will interrupt the circuit of the coil of the lineswitch LS1, whichthereupon opens, and cannot again be closed by reason of theinterruption of the circuit between conductors 52 and 57 by; the contactmember LS1in which bridges the differential relay switch contact member-The arrangement and operation of the interlocking contact members andcircuit for connecting the motor M#2 to the line and regulating thefield resistor FR2, correspond exactly-to the above-describedarrangement and operation for the motor M#1, the, re-

utilized sistor sections BB2 and RR3 be g o the re with the motor M#2 inplace sistor sections R2'and B3.

It willbe observed that the two motors m. independent of .each otherand, conseguently, onemay be connected to the line or braking somewhatahead of the other, although both will probably be-connected to the hneat about the same time.

- In the, present system, the P. K. control- 'lers remainin the finalposition, until the master controller is returned to its ofi po sitionby reason of the ener ation of the circuits of both actuating co of eachcontroller under the conditions just described, as about to be traced indetail. It will be understood that, if desired, suitable rovision may bemade to return the contro ers to their ofi positions, prior to suchmovementof the master controller, although such an action is notnecessary, since the main circuits are already opened by the lineswitches. The :air brakes will not be re-' leased, however, so long asthe mastercontroller occupies Lits braking"position. A single batterymay be utilized instead of a separate battery for each motor, but Iprefer the latter arrangement by reason of the fact that the batteryvoltage is found to increase rapidly when the motor is thrown on theline and, accordingly, if a single battery is relied upon for bothmotorsand one of the motors becomes connected to the line first, the batteryvoltage may be so varied, as to -ma,terially interfere with theoperation of automatic braking.

- cation of the air-brakes, or other a braking equipment of the vehicle,.whenever the electric retar eflort ceases or is tl weakened. resultsfrom the act t at, upon the loss of regenerated cur rent by reason ofthe trolley leaving the wire or other interruption of main-circuitconnections, which causes thel'ow-current limit switches A1 and A2 todrop and thus effeet the ope of the line switches LS1 and LS2, thfofiowing circuits are formed.

One circuit is continued from the conductor '8, which is energized fromthe master controller in either the braking or holding position, throughinterlock PK11 to 8, conductor 50, contact members DlBof thedifferential relay D1 in its lower position which corresponds to lowmotor voltage, conductor 54, contact members of the limit switch B1 inits lower position, conductor 55, interlock LSl-out, conductor 56, andactuating coil 99 of the inverted valve of the controller PKl to thenegatively-connected conductor 9. A further circuitis com leted from theconductor 54, through inter ock Isl-out, conductor 65, contact membersof the limit switch C1 in its lower position, conductor 58 and theactuating coil 100 of the standard valve of the controller PKI to thenegative conductor B. Since both actuating coils of the controller PKIare simultaneously energized, the controller moves rapidly from whateverposition occupied to the final position 8, in accordance withpreviously-stated principles.

Thus, the air-brakes are automatically actuc ated' in the mannerhereinbefore' set forth,

as soon as the controller reaches its last poholding position difiersfrom the brakingposition only in that the circuits of theinverted valvemagnet coils 99 are interrupted.

By this means, the progression of the PK controllers may be arrested atany point and 'socausethespeedofthevehicletod more slowly or continue ata constant speed if it is operating-down bill. This enables theoperator, by moving his controller from one position to theother, toregulate the rate of retardation or to hold any speed on down grade. Ina good many however,. it may be found advisable to omit the holdingPosition entirely and Pro ide on y for he Independently operatedswitches may be substituted, as above indicated, for the PK controllers,and it' may be found desirable toutilize separate resistances and, insome cases, separate line switches for governing the braking connectionsas distinguished, from the accelerating connections of the system.

In order to return to the line a larger proportion of the energynecessarily used in stopping a vehicle, the driving motors may first beconnected in multiple circuit relation until the vehicle speed ismaterially re duced and then connected in series relation, therebyenabling them to return energy to the line at a much lower speed, as setforth in my co-pending application, Serial No. 860,608, filed September8, 1914.

If the motors are used on a local schedule car or train, which stops sofrequently that the motors seldom attain, their full speeds,

it may be of advantage to connect the motor only in series during theregenerating period.

The circuit connections and the arrangement of the apparatus may, ofcourse, be

varied within the spirit andscope of my invention. The invention is, forexample, not limited to a two motor controller, nor to a system havingany specific arrangement of switches or motors, and I desire that onlysuch limitations be imposed as are indicated in the appended claims.

' Iclaim as my invention:

1. In a system of control, the combination with a supply circuit, anelectric motor having an armature and a field magnet winding connectedin series relation, afield regulating resistance adapted to be connectedin series with the field magnet winding and an auxiliary source ofenergy for exciting the field magnet winding, of automatic means forconnecting the motor to the supply circuit in order'to return energythereto and to retard the motor, when a predetermined voltage relationexists between the motor armature and the supply. circuit.

2. In a system of control, the combination with a supply circuit, anelectric motor having an armature and 'a field magnet winding connectedin series relation, and a field regulating resistance which is normallyshort circuited when the motor is in operation and is adapted to beconnected in series with the field magnet winding, of an auxiliarysource of energy and means for introducing the field regulating.resistance and connecting the auxiliary-source of energy across thefield and the regulating resistance, and automatic'means connecting themotor to the supply circuit in order to return energy thereto and toretard the motor, when a predetermined voltage relation exists betweenthe motor armature and the supply c cuit,

3. In a control system, the combination with a supply circuit, anelectric motor having an armature, and a field magnet winding, anormally short circuited field regulating resistance and means forseparately exciting the field magnet winding, of automatic means forregulating said resistance and connecting the motor to the supplycircuit when the voltage generated at the motor terminals exceeds thevoltage of the supply circuit.

4. In a control system, the combination with a supply circuit, a serieswound electric motor, a storage battery, a. field regulating resistanceand means for connecting the storage battery in shunt circuit relationto the field magnet winding and the field re lating resistance, ofautomatic means i dr connecting the motor to the su ply circuit when thevoltage generated at t e armature terminals bears a predeterminedrelation to the supply circuit voltage.

5. A control system, comprising a supply circuit, a plurality ofelectric motors and means for successively arranging the motors in aseries and in a multiple circuit relation for accelerating and operatingthe motors, and for independently establishing regenerative brakingcircuits for the several motors and maintaining substantially constantbraking currents as the motors are retarded;

6. A control system comprising a supply circuit, a plurality of electricmotors, means for either connecting the motors successively in a seriesand in a multiple circuit. relation for accelerating and operating themotors, or independently connecting the several motors to the supplycircuit for returning energy thereto and maintaining substantiallyconstant braking currents as the motors are retarded.

7 A control system, comprising a plurality of electric motors, controlmeans for effecting the acceleration and operation of the meters, 1 andother control means for regulating the field excitation of the motorsand severally connecting them to the supply circuit in order to returnenergy thereto.

8.- In a control system, the combination with a plurality of electricmotors, control means for effecting the acceleration and operation ofthe motors, and other control means for regulating the field excitationof the motors and severally connecting them to the supply circuit inorder to return energy thereto, of a single means for. governing t e twocontrol means.

, 9. In a control system, the combination with aplurality of electricmotors, control means for effecting the acceleration and operation ofthe motors, and other control means for regulating the field excitationof the motors and severally connecting them to t e supply circuit in'order to return energy thereto, of a master controller adapted to overnone of said control means when adusted in one direction and to governthe other set of control means when adjusted in the opposite direction.

10. In a control system, the combination with a plurality of electricmotors, control means for effecting the acceleration and operation ofthe motors, and other control means for regulating the field excitationof the motors and severally connecting them to the supply circuit, of 'amaster controller for governing the aforesaid control means, one of saidcontrol means embodying differential relay switches dependent upon apredetermined voltage relation between the supply circuit and thearmatures of the several motors for connecting the motors to the circuitin order to return energy thereto.

11. In a control system, the combination with a supply circuit, anelectric motor having an armature and a field magnet winding connectedin series relation, and a field regulating resistance, of an auxiliarysupply circuit adapted to be connected to the terminals of the fieldmagnet windings and its regulating resistance, and a differential relayswitch dependent upon a predetermined voltage relation between thesupply circuit and the motor armature for connecting the motor to thesupply circuit in order to return energy thereto when the motor isoperating as a generator.

12. A system of control comprising a supply circuit, an electric motorhaving an armature and a field magnet winding, means for controlling theacceleration and operation of the motor, a field regulating resistance,an auxiliary source of energy, means for controlling the regulatingresistance and connectingthe auxiliary source of energy across the fieldmagnet winding and its resistance and a master controller adapted tooccupy one series of positions for governing the accelerating andoperating control means and another set of positions for governing thecontrol means for the field regtilatingresistance and the auxiliarysource.

13. A control system comprising a supply circuit, an electric motorhaving an armature and a field magnet windingJa field regulatingresistance, an auxiliary source of energy and a differential relayswitch dependent npon a predetermined relation between the supplycircuit voltage and the voltage across the terminals of the armature anda master controller adapted to occupy one set of control positions forgoverning the acceleration and operation of the motor and another set ofcontrol positions for effecting the introduction and control of thefield re ulating resistance, the excitation of the field magnet windingfrom the auxiliary source and the connection of the motor to the supplycircuit for returning energy thereto, said last named connection beingdirectly dependent upon the differential relay switch.

14. A system of control comprising a supply circuit, a series motorhaving an armature and a field magnet winding, means for regulating thefield magnet winding, a storage battery connected in shunt circuitrela-,

tion to the field magnet winding and the regulating means and adapted toreceive energy from the armature circuit or deliver energy to the fieldcircuit according as the armature current is greater or less than thefield current.

15. A system of control comprising a supply circuit, a series motorhaving an armature and a field magnet winding, means for regulating thefield magnet winding, a storage battery adapted to receive energy fromor deliver energy to the armature and field circuit according as thearmature current is greater or less than the field current, and meansfor connecting the motor to the supply circuit to return energy theretowhen the motor is operating as a generator.

16. A system of control comprising a supply circuit, a series motorhaving an armature and a field magnet winding, a resistance connected inseries with the field magnet winding, a storage battery connected inshunt relation to the field winding and the from the motor circuit or tosupply energy to the field magnet winding accordin as the armaturecurrent is ater or less 1; an the field current when t e motor isconnected to the supply circuit for supplying energy thereto during thebraking period.

17. A system of control comprising a supply circuit, a series'motorhaving. an armature and a field magnet winding, a resistance connectedin series with the field-magnet winding, means for connecting the motorto the supply circuit to r'eturn energy thereto during the brakingperiod, means for regulating the resistance, a'storage bat,- teryconnected in shunt relation to the field winding and the resistance, andada ted to receive energy from the motor circuit or to supply energy tothe field magnet" winding according as the armature current is greateror less than the field current...

18. A system of control comprising a series motor having an armature anda field magnet winding, a mechanical brake apparat-us, means forconnecting the motor to the supply circuit to return energy theretoduring the braking period, means for regulating the excitation'of the.field, and means automatically dependent upon the regulating means foractuating the mechanical brake apparatus. a

19. A control system comprising a supply circuit, a series motor havingan armature and a field magnet winding, a mechanical brake apparatus, anauxiliary source of energy and a regulating means for graduallystrengthening the motor field to maintain a su stantially constantbraking current and to return energy to the supply circuit, and meansdependent upon the fiel regulating means for automatically actuating themechanical brake apparatus.

20. A control system comprising a supply circuit, a series motor havingan armature and a field magnet winding, a mechanical brake apparatus,means for regulating the field magnet winding, a storage batteryconnected in shunt relation to the field magnet windingandthe regulatingmeansand means for connecting the motor to the circuit to return energythereto during the braking period, said regulating means being adaptedto hold the braking current substantially constant until the motor fieldis strengthened to a predetermined extent and to then actuate themechanical brake apparatus.

21. A control system comprising a supply circuit, a mechanical brakeapparatus, a series motor adapted'to return energy to the supplycircuit, and means for gradually strengthening the motor field as itsspeed is reduced, and automatic -means dependent upon saidfieldregulating means to actuate the mechanical brake apparatus.

22. A system of control comprising a supply circuit, a series motorhaving an armature and a field magnet winding, a mechanical brakeapparatus, a resistance connected in series with the field magnetwinding,

means for connecting the motor to the supply circuit to return energthereto during the braking period, means for regulating the resistance,a storage battery connected in shunt relation to the field winding andthe resistance and adapted to receive energy from the motor circuit orto sup 1y energy tothe field magnet win acco as the armature current isgreater or less t an the field current, and automatic means dependentupon the resistance regulating means for actuating the mechanical brakeapparatus.

23. In a control system, the com ination with a series wound electricmotor, a mechanical brake-apparatus, and means for establishing aregenerative braking circuit and maintaining a substantially constantbraking current as the motor is retarded, of means for automaticallyactuating the mechanical braking apparatus at a predetermined point inthe retardation of the motor.

field pg-gust winding, a variable resistance,

an a my source of current, means for 24. A system of control for anconnectin the said source and said resistance in circuit with the fieldma et winding, means for regulating the sa1d variable resistance inaccordance with the current and electromotive force generated by themotor armature, and means for connecting the motor to the supply circuitwhen the voltage generated by the motor armature attains a predeterminedvalue.

25. A system of control for braking an electric motor comprising asupply circuit, an electric motor having series connected armature andfield magnet windings, a variable resistance, an auxiliary source ofcurrent, means for connecting the said source and said resistance incircuit with the field magnet winding, means for automaticallyregulating the said variable resistance in accordance with the currentand electromotive force generated by the motor armature, and means forautomatically connecting the motor to the supply circuit when thevoltage generated by. the motor armature attains a predetermined value.

4 26. A system ofcontrol for braking an electric motor comprising asupply circuit, an electric motor having an armature and a field magnetwinding, a variable resistance, an auxiliary source of current, meansfor connecting the said source and said resistance in circuit with thefield magnet winding, means for automatically connecting the motor tothe supply circuit when the voltage generated by the motor armatureatance in circuit-with the field magnet winding, means for automaticallyconnectin the motor to the supply circuit when thevo tag'e generatedby te-motor armature attains a predetermined value, means for regulating thesaid variable resistance, and means controlling said regulating meanswhereby the current generated by the motor is maintained betweenredetermined values until the motor speed as diminished below apredetermined value. a

28. A system of control for braking an electric motor comprising asupply circuit, an electric motor having an armature and a field magnetwinding, a variable resistance,

an auxiliary source of current, means for connecting the said source andsaid resistios ance in circuit with the field magnet winding, means forautomatically connectin the motor to the supply circuit when the v0 tagegenerated by the motor armature attains a predetermined value and meansfor regulating the said variable resistance to maintain the currentgenerated by the motor armature in excess of a predetermined value untilthe motor speed has diminished below a predetermined value.

29. A system of control for braking-an electric motor comprising asupply circuit, an. electric motor having an armature and a-field magnetwinding, a variable resistance, an auxiliary source ofcurrent, means forconnecting the said source and said resistance in circuit with the fieldmagnet winding, means for automatically connect ing the motor to thesupply circuit when the voltage generated by the motor armature attainsa ,,predetermined value, and means for regulatihg the said variableresistance to maintain the current generated by the motor armaturebetween predetermined values until the motor speed hasdiminished below apredetermined value.

30. A system of control for bralring an electric motor comprising asupply circuit .means for anelectric motor having an armature an 1 afield magnet winding, a-variable resistance, an auxiliary. source ofcurrent, means for connectin the said source and said resistance incircuit with the field magnet winding, means for automatically'connect--' duced when the current generated by the motor armaturediminishes below a redetermined value and whereby the e ective value ofsaid resistance is increased-when the current generated by the motorarmature exceeds a predetermined'value.

31. A system of control for electric motor comprising'a supply circuitan electric motor having an armature a field magnet winding connected inseries relation, an auxiliary source of current, means for connectingthe said source in circuit with the field magnet winding, and regulatingthe current in the field magnet win ng of the motor to maintain thecurrent generated by the motor armature between redetermined valuesuntil the motor diminishes below a predetermined value. a

32; A system of control for an electric motor comprising a supplycircuit,

an -electric motor having an armature and a.v

braking an of one field magnet winding, an auxiliary source of current,means for connecting the said source in circuit with the field magnetwinding, and automatic means for regulatin the current in the -fieldmagnet winding 0 the motor to maintain the current nerated in the motorarmature in excess 0 a redetermined value until the motor spee minishedbelow a redetermined value.

33. A system 0 control for braking an electric motor comprising anelectric motor having an armature and a field magnet winding, anauxiliary source of current, means for connecting the said source incircuit with thefield magnet winding, a reversing switch for reversingthe connections of the motor field magnet winding with rehas dispect toits armature, and means for actuated current for automatically applyingthe mechanical braking means.

35. In a system of control, the combinetion with a supply circuit, anelectric motor havin an armature and a field magnet winding, 0 automaticmeans for connecting the motor to the supply determined relativecbnditions of the motor circuit and the supply circuit in order toreturn energy thereto and for maintaining said relative conditions.

circuit under pre- 36.- In a system of control, the combination with'asupply circuit, anelectric motor having an armature and a field ma etwindin connected in series relation, a eldregulahngresistance adapted tobe connect ed in series with the field magnet winding,

and an auxiliary source of ener forexciting the field magnet winding, 0automatlc means for connecting the motor to the supply' circuit forcircuit.

tor circuit and the supply motor having an armature and a'. field magnetwinding in series relation and a field-regulating resistance: which isnor tion of the field magnet win rgy, means. for introducing e erationthereto under I predetermined relativeconditions of the mems ng: ti b fan' sunk"; "soureej regenera ve rak1ng,o fi

regulating resistance and connecting-the 111 7. If acrossthe iin zgdi iinam e and.

115. 87.111 a system oicontrol, the combine-'1. 'tion with a supplycircuit and an electric automatic means for connecting the motor "to thesupply circuit in order to return en ergy thereto and retard the motorunder predetermined conditions.

38. In a control system the combination with a supply circuit, anelectric motor having an armature and a field magnet winding, a normallyinactive field-regulating device, and means for separately exciting thefield magnet winding, of means for operatively connecting saidfield-regulatin device and the excitin means in circuit uringregeneration an automatic means for regulating said device in accordancewith the regenerated current.

39. In a control system, the combination with a supply circuit anelectric motor having an armature and a field magnet winding, a normallyinactive regulating device and means for separately exciting the fieldmagnet winding, of automatic means for governing the operation of saidfield-regulating device and for connecting the motor to the su plycircuit under predetermined relative electrical conditions of said motorand said supply circuit.

40. In a control system, the combination with a supply circuit, aplurality of electric motors, means for controlling said motors duringacceleration and means for independentl establishing regenerativebraking circuits or said motors, of means for independently governingthe operation of said motors during the regenerative period.

41.In a control system, the combination with a supply circuit and anelectric motor adapted to be operated as a generator, of means forarranging the motor circuits for generator operation, means forautomatically connecting said motor to a supply circuit underpredetermined circuit conditions, and means for utomatically maintaininga substantially constant braking current as the motor is retarded.

42. A control system comprising a supply circuit, a plurality ofelectric'motors, and means for governing said, motors durin motoroperation, of means for indepen ently and automatically establishingregenerative brakin circuits for said motors.

43. a control system, the combination with a lurality of electricmotors, means for control ing said motors during motor operation andothermeans for controllin said motors during regenerative braking,automatic means for connectin said motor to the supply circuit under preetermined condi tions and for maintaining said conditions, and manuallyofierated means forgoverning said two contro ing means.

44. In a control system, the combination with a plurality of electricmotors, means for control ing said motors durin motor operation andother means for regu ating the field excitation of said motors andconnecting them to a supply circuit, of means for governing saidcontrolling means, one of said controlling means embodyingelectro-responsive apparatus for connecting the motors to the supplycircuit in order to retur' their energy thereto.

45. A system of control comprising a supply circuit a series motorhaving an armature and field magnet windin means for regulating theexcitation of sai' winding, an energy-accumulating device adapted toreceive energy from or deliver energy to the armature andfield circuitin accordance with predetermined current conditions,and automatic meansfor connecting the motor to the supply circuit for returning energythereto vlhen the motor is operating as a gener a or.

46. A system of control comprising a supply circult a series motorhaving an armature and field magnet winding, means for regulating theexcitation of said winding, a storage battery connected in multiplerelatron to said winding and said regulating me ns and adapted tobe-charged or discharged in accordance with predetermined currentconditions, and automatic means for connecting the motor to the supplycircuit for returning energy thereto.

47. A system of control comprising an electric motor having an armatureand field magnet winding, an auxiliary braking means, means forconnectingzthe motor to a supply circuit for regenerative braking, andmeans for actuating said auxiliary braking means under predeterminedconditions of regenerative braking.

48. A system of control comprising an electric motor having an armatureand field magnet winding, an auxiliary braking means, means forconnecting the motor to a supply circuit for regenerative braking, meansfor regulating the excitation of said field mag net winding duringregenerative braking, and means dependent upon the operation of saidregulating means for effecting the operation of said auxiliary brakingmeans.

49. A system of control comprising an electric motor having an armatureand field magnet winding, a normally inoperative fluid-operated brakingapparatus, means for connecting the motor to a supply circuit forregenerative braking thereto, automatic means for regulating-theregenerative braking operation, and means dependent upon predeterminedconditions of said regenerative braking operation for rendering saidfluid-operated braking apparatus effective.

50. A control system comprising a supply circuit, an electric motorhaving an armature and a field magnet winding, auxiliary braking means,means for regulating the field strength of said motor when operating asa generator for maintaining predetermined dynamic braking conditions,and means deoendent upon the position of said regulating means .foractuating said auxiliary braking means.

51. A control system comprising a supply circuit, an auxiliary brakingmeans, a series motor adapted to return energy to the supply circuit,means for varying the motor field strength as the speed of the motorchanges, and means indirectly dependent upon the speed of the motor foractuating said auxiliary braking means.

52. A control system comprising a supply circuit, an auxiliary brakinmeans, a series motor adapted to return energy to the supply circuit,means for increasing the excitation of the motor field as the speed isreduced, means dependent upon said last means for actuating saidauxiliary braking means, and means dependent upon predeterminedregenerative current conditions for disconnecting said motor from saidsupply circuit.

53. In a control system, the combination with an electric motor, anauxiliary braking means, and means for establishing a regenerativebraking circuit and maintaining a substantially constant braking currentas the motor is retarded, of means for actuating the auxiliary brakingmeans at a predetermined point in the retardation of the motor, andmeans for discontinuing the regenerative braking action.

54. A system of control for braking an electric motor comprising asupply circuit, an electric motor having an armature and a field magnetwinding, a variable resistance, an auxiliary source of energy, means forconnecting said source and said resistance in circuit with the fieldmagnet winding, automatic means for regulating saidvariable resistancein accordance with predetermined circuit conditions, and means forconnectpredetermined relative conditions of said motor and said supplycircuit.

55. A system of control for braking an electric motor comprising asupply circuit,

said motor having an armature and field magnet winding, an auxiliarysource of en-, ergy adapted to excite said field winding during thebraking operation, an automatic means for regulating the braking currentbetween predetermined values until a predetermined motor speed isattained.

56. A electric motor comprising a supply circuit, a motor having an.armature nd field magnet winding, an auxiliary source of energy adaptedto excite said field winding during the braking operation, anelectro-responsive means for regulating the braking current andmaintaining it in excess of a predetering the motor to the supplycircuit under ing, a. regulating system ofcontrol for braking an memesmined value until a speed is obtained.

57. A system of control for braking an electric motor comprising asupply circuit, a motor having an armature and field magnet Winding, anauxiliary source of energy adapted to excite said field winding duringthe braking operation, means for reversing the field magnet winding andmeans independent of the previous position of said reversing means foractuating said reversing means when the motor is changed to a brakinggenerator.

58. .A system of control comprising an electric motor adapted to beoperated as a braking generator having an armature and field magnetwinding, means for reversing the field magnet winding with respect toits armature, and means for actuating said reversing means when themotor is changed to a braking generator irrespective of the position ofsaid reversing means.

59. The combination with an electric motor, a load driven thereby, andmeans for effecting regenerative braking of said motor, of auxiliarybraking means adapted to be actuated under predetermined conditionswhich are independent of the motor circuit.

60. A control system comprising an electric motor adapted to be operatedas a generator and having an armature and field magnet winding, aregulating resistance in circuit with said winding, 9. battery connectedacross said winding and regulating resistance, means for automaticallyconnect; ing said motor to a supply circuit under predetermined circuitconditions, and means for temporarily inserting resistance into the motor circuit subsequent thereto.

61. A control system comprising an electric motor adapted to be operatedas a braking generator, means for connecting said motor to a supplycircuit under predetermined circuit conditions, and automatic meansfortemporarily inserting resistance into said motor circuit.

62. A control system comprising a supplycircuit, an electric motoradapted to be operated as a braking generator, said motor having anarmature and field magnet windresistance in circuit with predeterminedmotor said winding, an connected across said regulating resistance andsaid winding, means for connectin said motor to said supply circuitunder pre etermined circuit conditions, and means for causing a portionof said regulating resist ance to be temporarily inserted in the motorcircuit subsequent to its connection to the supply circuit.

63. A control system comprising a sup- -ply circuit, an electric motoradapted to be operated as a braking generator and having auxiliarysource of energy an armature and field magnet winding, I

alumna means for connecting said motor to said supply circuit, andautomatic means for temporarilg limiting the generated current.

64. control system comprising a supply circuit, an electric motoradapted to be op erated as a braking generator, and automatic means forraising the generated voltage to a predetermined relation to the voltageof said supply circuit and subsequently connecting said motor thereto.

a 65. A control system comprising a supply circuit, a plurality ofelectricmotors adapted to be operated as braking generators, a pluralityof means for automatically and independently effecting predeterminedrelative voltage conditions between said supply circuit and said motorsprior to connecting said motors thereto.

66. A control system comprising a supply circuit, a plurality ofelectric motors adapted to be operated as braking generators, aplurality of means for automatically and independently efi'ectingpredetermined relative voltage conditions between said supply circuitand said motors and for subsequently and independently connecting saidmotors to said circuit.

-to the voltage of a supply 67. In a control system, the combinationwith a supply circuit, an electric motor having an armature and fieldmagnet winding, a regulating resistance in circuit with said winding,and means for maintaining a substantially constantvoltage acrossvsaidfield winding and said regulating resistance when said motor is actingas a braking generator, of automatic means for connecting said motor to'said supply circuit under predetermined relative voltage conditions ofsaid supply circuit and said motor.

68. The method of operating an electric motor as a braking generatorwhich consists in raising the enerated volta e of said motor above theV0 tage of. a supp y circuit, connecting said motor to said supplycircuit, temporarilyinserting resistance'in the motor circuit andsubsequently regulating the braking current.

69. The method of operating a plurality of electric motors as brakingpendently raising the voltages of said motors to a predetermined valuewithrespect circuit and independently connecting sai motors thereto.

70. In a system of control, the combination with a supply circuit and adynamoelectric machine. ada ted for regenerative braking, of auxiliaryraking means, means for regulating the field strength of said machinefor normally maintaining predetermined regenerative conditions, meansfor interrupting the supply-circuit connection under certain abnormalconditions, means for thereupon actuating said regulating m'eansgenerators which consists in automatically and inde to a predeterminedposition, and means for then rendering said auxiliary braking meanseffective.

71. In a system of control, the combination with a supply circuit and adynamo- ,electric machine adapted for regenerative braking, of amechanical brake apparatus, means for regulating the system to normallymaintain substantially constant regenerative conditions, means forinterrupting the supply-circuit connection upon a loss of regenerativecurrent, means for thereupon actuating said regulating means to apredetermined position, and means dependent upon such a actuation foreffecting the operation of said brake apparatus 72. In a system ofcontrol, the combination with a supply circuit and a'dynamoelectricmachine adapted for regenerative braking, of a mechanical brakingapparatus, means for automatically actuating said apparatus underpredetermined regenerative braking conditions, and. means dependent uponthe results of such actuation for rendering the regenerative brakingsystem inoperative. i

73. In a system of control, thecombination with a supply circuit. and adynamoelectric machine adapted for regenerative braking, of amechanical'braking apparatus, means for automatically actuating saidapparatus underv predetermined regenerative conditions, and relay meansactuated in acdependent regenerat ve operation, of means forautomatically raising the voltages of said machines to predeterminedvalues, and rela means for thereupon connecting the mac ines to saidsupply-circuit independentlyfof each other. Y

76. In a system of control, the combination with a supply circuit and aseries-wound dynamo-electric machine adapted for regenerative operation,of means for automatically raising the volta e of said machine to apredetermined va ue, and means for thereupon automatically connectingthe machine to said supply circuit.

77. In a system of control, the combina tion with a. supply circuit anda dynamo- .electricmachine adapted for regenerative operation, ofauxiliary exciting means for subscribed my name this fourth day ofOcautomatically raising the voltage of said tober,1912.

machine to a predetermined value, and re- NORMAN'W. STORER. lay meansfor thereupon automatically con- Witnesses: 5 necting the machine tosaid supply circuit. 0. BIELER,

In testimony whereof, I have hereunto B. B. Hume.

